The need to monitor, on a frequent and continuous basis, the vital signs associated with hospitalized patients particularly those who are seriously ill is an important aspect of health care. Virtually every hospitalized patient requires periodic measurement in logging of blood pressure, temperature, pulse rate, etc. Such monitoring has typically been performed by having a health care worker periodically visit the bedside of the patient and measuring and/or observing the patient's vital signs using dedicated equipment that is either hooked up to the patient or brought into the patient's room. Such a monitoring procedure is not ideally cost-effective because of its being highly labor intensive.
A great many implantable medical devices (IMDs) for cardiac monitoring and/or therapy whose sensors are located in a blood vessel or heart chamber and coupled to an implantable monitor or therapy delivery device are used for diagnosis and therapy. Such systems include, for example, implantable heart monitors, therapy delivery devices, and drug delivery devices. All these systems include electrodes for sensing and sense amplifiers for recording and/or deriving sense event signals from the intracardiac electrogram (EGM). In current cardiac IMDs that provide a therapy, sensed event signals are used to control the delivery of the therapy in accordance with an operating algorithm. Selected EGM signal segments and sensed event histogram data or the like are stored in an internal RAM for telemetry to be transmitted to an external programmer at a later time. Efforts have also been underway for many years to develop implantable physiologic signal transducers and sensors for temporary or chronic use in a body organ or vessel usable with such IHMs for monitoring a physiologic condition other than, or in addition to, the disease state that is to be controlled by a therapy delivered by the IMD.
A comprehensive listing of implantable therapy devices are disclosed in conjunction with implantable sensors for sensing a wide variety of cardiac physiologic signals in U.S. Pat. No. 5,330,505, incorporated herein in its entirety by this reference.
Typically, an IHM measures blood pressure and temperature signal values which stem from changes in cardiac output that may be caused by cardiac failure, ventricular tachycardia, flutter or fibrillation. These variations may reflect a change in the body's need for oxygenated blood. For example, monitoring of a substantial drop in blood pressure in a heart chamber, particularly the right ventricle, along or in conjunction with an accelerated or chaotic EGM, was proposed as an indicator of a fibrillation or tachycardia sufficient to trigger automatic delivery of defibrillation or cardioversion shock. More recently, it has been proposed to monitor the changes in blood pressure by comparing those values that accompany the normal heart contraction and relaxation to those that occur during high-rate tachycardia, flutter or fibrillation.
A number of cardiac pacing systems and algorithms for processing monitored mean blood pressure or monitored dp/dt have been proposed and in some instances employed clinically for treating bradycardia. Such systems and algorithms are designed to sense and respond to mean or dp/dt changes in blood pressure to change the cardiac pacing rate between an upper and a lower pacing rate limit in order to control cardiac output. Examples of IHMs blood pressure and temperature sensors that derive absolute blood pressure signals and temperature signals are disclosed in commonly assigned U.S. Pat. Nos. 5,368,040, 5,535,752 and 5,564,434, and in U.S. Pat. No. 4,791,931, all incorporated by reference herein.
The Medtronic® Chronicle™ Implantable Hemodynamic Monitor (IHM) disclosed in U.S. Pat. Nos. 6,024,704 and 6,152,885, both incorporated herein by reference in their totality, employ the leads and circuitry disclosed in the above-incorporated commonly assigned U.S. Pat. Nos. 5,535,752 and 5,564,434 patents to record absolute blood pressure values for certain intervals. The recorded data is transmitted to a programmer under the control of a physician in an uplink telemetry transmission from the IHM during a telemetry session initiated by downlink telemetry transmission from the programmer's radio frequency (RF) head and receipt of an integration command by the IHM. Thus, in accordance to the '704 and '885 patents, a method is disclosed in which an IHM is used for deriving reference and absolute pressure signal values using implantable physiologic sensors to detect relative cardiac pressure signal values for storage and transmission.
Further, in accordance with the '704 and '885 patents, calibration of the reference pressure and/or temperature sensors in relation to an external calibrated barometric pressure and/or body temperature sensors could be accomplished. In addition, the same system may be used to interlace digital signal values related to pulmonary artery diastolic pressures with the primary cardiac pressure signal values derived from the right ventricle as disclosed in U.S. Pat. No. 6,155,267, incorporated herein by reference.
Heart failure is a progressive disease. While treatment slows the progression of the disease, current technology does not provide a cure. The best treatment regimen available to date is a combination of continuous diagnosis and drug therapy. Once a heart failure patient is in the hospital, current technology does not provide a continuous means of monitoring the patient during their stay in the hospital. Current practice is based on a dedicated programmer that is used to gain access to the pressure waveforms. Only trained physicians can currently uplink the data, and this is available only when such a trained physician is present, and is therefore not available on a continuous basis.
The present invention enables continuous remote monitoring of patients. In sharp contrast, prior heart failure management involves taking measurements of a few variables in the clinic with accurate catheterization pressures taken only occasionally because of the difficulty of obtaining them.
Accordingly, there is a need to provide continuous and reliable measurements over sustained long period of time. Further, emerging trends in health care including remote patient management systems require that the IMD/IHM be compatible with communication systems, including the Internet, the worldwide web, and similar systems to provide real-time communications and data exchange between the IHM in a patient and a remote center where physicians and other experts reside.